There is known an in-vehicle internal combustion engine provided with a supercharger of an exhaust turbine driven type (i.e., turbocharger), aiming at high power output of the engine or the like.
JP-2000-345852A discloses a system which controls a supercharging pressure of intake air supercharged by this supercharger. This system is so structured that a waste gate valve (WGV) is located in an exhaust bypass passage bypassing an exhaust turbine to feedback-control an opening of the WGV in such a manner as to make an actual supercharging pressure detected by a supercharging pressure sensor be equal to a target supercharging pressure for controlling a quantity of an exhaust gas to be supplied to the exhaust turbine. This controls a rotational speed of a compressor rotating integrally with the exhaust turbine to control the actual supercharging pressure to be the target supercharging pressure.
As shown in FIG. 3, in a normal supercharging pressure control system, an actual supercharging pressure varies to some extent in a linear relation with a change in a WGV control signal (control duty value “Duty” of an electromagnetic valve for driving the WGV) for controlling an opening of the WGV. However, in a supercharging pressure control system where a foreign object such as oil adheres inside the electromagnetic valve for driving the WGV, a changing characteristic of the actual supercharging pressure to the change in the WGV control signal varies in a partial region, so that a linearity in the changing characteristic of the actual supercharging pressure to the change in the WGV control signal possibly deteriorates. Occurrence of such an abnormality possibly causes deterioration in controllability of the supercharging pressure control.
The above-mentioned supercharging pressure control system compares a deviation between the actual supercharging pressure and the target supercharging pressure and a feedback correction amount calculated based upon the deviation with respective predetermined determination values to determine presence/absence of failures of components used for the supercharging pressure control. However, since the changing characteristic of the actual supercharging pressure to the change in the WGV control signal is not taken into account at all, it is not possible to detect abnormality (deterioration in linearity or the like) in the changing characteristic of the actual supercharging pressure.
In addition, there is proposed an engine with a supercharger having a structure equipped with a supercharging state varying apparatus for adjusting a supercharging state of the supercharger. As one example, there is the technology in which a bypass passage is located so as to bypass an intake compressor disposed in an intake passage and also an air bypass valve (ABV) as a bypass valve is arranged in the bypass passage. For example, when a throttle valve is operated to be fully closed in a supercharging state by a turbocharger, since pressures in an intake pipe at an upstream side of the throttle valve (throttle-upstream-pressure) excessively increase, the air bypass valve is opened for reduction in pressures in the intake pipe at the upstream side of the throttle valve. On this occasion, opening the air bypass valve results in the solution for various problems such as occurrence of surge noises by the intake compressor or damages of the intake pipe or the like caused by an excessive increase in the throttle-upstream-pressure.
The air bypass valve is generally arranged in such a way that movement of a valve body in the air bypass valve causes the bypass passage to be opened or closed. However, when the valve body is stuck by involvement of foreign objects or attachment of oil or the like, the air bypass valve cannot be operated to be opened (valve-closing abnormality occurs). When such abnormality in the air bypass valve occurs, the throttle-upstream-pressure excessively increases at a fully closed state of the throttle valve, resulting in problems such as occurrence of surge noises or damages of the intake pipe or the like. Therefore, for the solution of the above problems, there is a hope for the technology which is capable of properly detecting abnormality in the air bypass valve at the time of occurrence of the abnormality thereof.
In view of the above, there exists a need for an apparatus and a method of an abnormality diagnosis for a supercharging pressure control system which overcome the above mentioned problems in the conventional art. The present invention addresses this need in the conventional art as well as other needs, which will become apparent to those skilled in the art from this disclosure.